Semi-conducting polymer system comprising a copolymer of ethylene-ethylarcralate or vinyl acetate,ethylene-propylene-termonomer and carbon black

ABSTRACT

Semi-conducting compositions of (i) a copolymer of ethyleneethyl acrylate or ethylene-vinyl acetate, (ii) an ethylenepropylene-termonomer elastomer, and (iii) a conducting carbon black.

nited States Patent 11 1 Lloyd et a].

[ NOV. 19, 1974 SEMI-CONDUCTING POLYMER SYSTEM COMPRISING A COPOLYMER OFETI-IYLENE-ETI-IYLARCRALATE OR VINYL ACETATE,ETHYLENE-PROPYLENE-TERMONOMER AND CARBON BLACK Inventors: Keith AndrewLloyd, Plainfield;

Eugene Jay Fisher, Brunswick, both of NJ.

Assignee: Union Carbide Corporation, New

York, NY.

Filed: Sept. 26, 1972 Appl. 310.; 292,338

US. Cl. 252/511, 260/37 R, 260/897 B Int. Cl. H0lb 1/04, C09b l/48 Fieldof Search 252/511; 260/897 B, 37 R Primary Examiner-Carl D. QuarforthAssistant Examiner-R. E. Schafer Attorney, Agent, or Firm-Francis M.Fazio [57] ABSTRACT Semi-conducting compositions of (i) a copolymer ofethylene-ethyl acrylate or ethylene-vinyl acetate, (ii) anethylene-propylene-termonomer elastomer, and (iii) a conducting carbonblack.

5 Claims, No Drawings SEMI-CONDUCTING POLYMER SYSTEM COMPRISING ACOPOLYMER OF ETI-IYLENE-ETHYLARCRALATE OR VINYL ACETATE,ETHYLENE-PROPYLENE-TERMONOMER AND CARBON BLACK BACKGROUND OF THEINVENTION Semi-conductingcompositions containing an ethylene polymer anda conducting carbon black have long been known and used in themanufacture of electrical conductors. These compositions have varied intheir polymers content and have included mixtures of polyethylene withvarious polymers such as ethylene-ethyl acrylate, ethylene-vinylacetate, ethylene-propylenehexadiene copolymers, and the like. In orderto overcome the undesirable properties imparted to the composition bythe presence of the large amounts of the carbon black required to makethe composition semiconductive it has been found desirable to employthose ethylene copolymers having high comonomer contents to achieve thecorrect balance of physical and conductive properties. The literature isreplete with such compositions and in this regard one can mention, as apartial listing, US. Pat. No. 3,178,384, U.S. Pat. No. 3,510,448 andGerman Offenlegungschrift No. 1,719,251. The use of such semi-conductingcompositions, the manner of their preparation and their desiredproperties are so well known and described in the literature, as alsoare their deficiencies, that no further discussion is required here toenable one skilled in the art to understand how the polymer componentsare produced and used in the preparation of the semiconductingcompositions.

DESCRIPTION OF THE INVENTION It has been found that certain specificethylene copolymer compositions having a low comonomer content, eitherby direct polymerization or by blending, when combined withethylene-propylene-termonomer terpolymers and conducting carbon black,yield semiconducting compositions that not only have the desiredphysical properties but are suprisingly improved in deformationresistance, solvent resistance, and conductivity when compared toheretofore known compositions which utilized ethylene copolymers havinga high comonomer content. The compositions of this invention haveover-all improved properties, a completely unexpected and unobviousfinding.

The ethylene copolymers useful in this invention are the copolymers ofethylene and a comonomer which is either ethyl acrylate or vinylacetate. The comonomer is present in the ethylene copolymer molecule ata critical concentration of from 2 to weight per cent, preferably from 3to 5 weight per cent. The ethylene copolymers and the methods for theirproduction are well known to those skilled in the art and do not requireextensive description herein. It will suffice to say that they areproduced by polymerization at elevated temperature and pressure incontact with a known free radical initiator. The copolymers are thosethat preferably have a melt index below 3.5 decigrams per minute andmore preferably from 0.5 to 2 decigrams per minute.

The ethylene-propylene-termonomer terpolymers are also well known andmany are commercially available. The termonomer component of theseelastomeric terpolymers can be 1,4-hexadiene, dicyclopentadiene,

methylcyclopentadiene, 5- ethylidenebicyclo[2.2.1lhept-Z-ene, or anyother termonomer known in the art as suitable. The terpolymers usually28 from to 35 weight per cent propylene and from 1.5 to 10 weight percent termonomer in the molecule. Their production is disclosed, forinstance, in US. Pat. Nos. 2,699,457, 2,930,781, 3,933,480, 3,000,866,3,000,867, 3,033,835, 3,063,973, 3,093,620, 3,162,620 and3,211,709.

The conducting carbon blacks are well known and any suitable form can beused, including oil furnace blacks or acetylene blacks, provided thatthey are conducting.

The conventional additives, in the conventionally used quantities, canbe present in the semi-conducting compositions of this invention. Theseinclude additives such as stabilizers, antioxidants, pigments,lubricants, ultraviolet stabilizers, antiblock agents and the like, andthey are added by the known procedures. Also present can be smallamounts of other polymers.

The semi-conducting compositions of this invention contain from 3 toweight percent, preferably from 5 to 15 weight percent, of theethylene-propylenetermonomer terpolymer and from to 50 weight percent,preferably from to weight percent, of the conducting carbon black, withthe balance being the ethylene-ethyl acrylate or ethylene-vinyl acetatecopolymer.

The semi-conducting compositions of this invention can, unexpectedly,withstand higher cable operating temperatures and are less subject toattack by solvents; they are characterized, generally, by lowtemperature coefficients of resistivity, low heat distortion values.high solvent resistance and good extrudability properties. All of theseproperties are important in insulation shielding compositions for powerconductors.

A low temperature coefficient of resistivity is desired in asemi-conducting composition to permit use at higher operatingtemperatures. Use of higher operating temperatures is the current trendin this field and at the higher temperatures the compositions experiencelarger decreases in conductivity with concomittant increases intemperature coefficient of resistivity. The instant compositions havelow temperature coefficients of resistivity and thus can be used at thehigher operating temperatures.

A low heat distortion value is desirable to minimize the volumetricexpansion of the semi-conducting composition and thus minimize thepossibility of dislocation or separation of the concentric neutral inthe cable structure and the disruption of its function. High solventresistance is an important factor where the cable is buried in theground or comes into Contact with motor oils, transformer oils, woodpreservatives, or any other solvent. Migration of solvent into thepolymer can occur under such circumstances and the swelling causesdimensional changes in the spacing of the carbon particles causing anundesirable increase in the resistivity of the semi-conductingcomposition.

Good extrudability is important not only from the point of view ofesthetics but also the ability to extrude smoothly generally results inthe formation of a better bond between the semi-conducting compositionand the adjacent surface.

The increased service demands on the distribution cables such as higheramperages and higher temperatures can be aecomodated by the use of thesemiconducting compositions of this invention.

In the following examples the test procedures used were those known inthe art. Brittleness was detera high ethyl acrylate content but did notcontain terpolymer. Control D A semi-conducting composition was preparedusing mined by ASTM D-746; secant modulus, tensile 5 parts of p y yhaving a melt index of 20 strength, and elongation by ASTM D638; andvolume dgm/min and l Parts Of the Same lcrpolymcl 36 resistivity by ASTMD-257. Re i t to ASTM N parts ofthe same carbon black and 0.2 part ofthesame 3 oil was determined by calculating the percent weight StabilizerUsed to P P the Composition of Example change after immersion in the oilat 23C. for periods Thls Control did not contain the P X'I of 1 day and7 days. Melt index of the polymers and 10 ThC PI'OPCI'UCS of each ofthese compositions are set Compositions was determined by ASTM D4238 andforth in the table below. In this t rst series ASTM lZlo. dfinsity byASTM D4505. 2 Oil was used in determining Oll resistance at 23 C. afterone day; stress cracking was determined by ASTM D-732 with the number ofsamples failing after EXAMPLE 1 2 days of submersion of samples in thedetergent solution being reported; the deformation was determined sg ifsg gg LE ;g gs ig g using a 10 kilogram load on a 0.5 inch stack ofinch ethyleneethyl acrylate copolymer having a melt index diameterspec-lmens' of] 5 dgm /min and an average ethyl acr late content The(ima m the table Indicates that Semi- Of a'bout g' p Cent 10 parts ethlene 20 conducting composition of Example 1 has improved p py 4hexadiene p y wherein ratio low temperature brittleness when compared toany of of each componem is 72 7 36 parts of a Com Controls A to D;improved elongation and lower secant ductive oil furnace carbon blackhavin an avera e armodulus when compared to Controls B and D; ml f 26 t30 2 proved stress crack resistance when compared to Con- [C e size 0 0mi imicrons an part 0 p0 trol B; and improved deformation attemperatures '9i A mm below- 100C and oil resistance when compared tonon of the composition was molded mto test plaques Controls A and C andevaluated.

For comparative purposes a series of semiconductive EXAMPLE 2 wasproduced m the Same manner as 30 A mixture of 29.8 parts of anethylene-ethyl acrylate below copolymer having a melt index of 0.]dgm/min. and an Comm! ethyl acrylate content of 1.5 to 2 weight per centwith A semi-conducting composition was prepared using 149 parts of aSecond ethylene ethy| acrylate copoly 53.8 parts ot an ethylene-ethylacrylate copolymer havmer having a melt index of dgm/mm and an ethyl inga melt index of 4.5 dgm./min. and an ethyl acrylate 35 acrylate Comem f12 to 13 weight cem was Content weight P cent and 10 Parts of the pared;this mixture had an average ethyl acrylate consume tcrpolymcr' 36 Partsof the Same Carbon black tent of about 2.4 weight per cent. The mixtureof ethyand 0.2 part of the same stabilizer used in Example I. |ene ethy1acrylate copolymers was bk d d i h 20 ln this control the ethylenecopolymer had a high ethyl parts f the terpolymer 3 pans f the Carbon lk acrylate Content 40 and 0.2 part of the stabilizer used in Example 1to pro- Conlml B duce a semi-conducting composition having the porp- Asemi-conducting composition was prepared using erties Shown i h bl 63.8parts of the same copolymer, 36 parts of the same carbon black and 0.2part of the same stabilizer used EXAMPLE 3 to prepare the composition ofExample I. This control 5 A id i g ition wa produ ed as ded d n lIil ncrpolym scribed in Example I using 44.8 parts of an ethylenevi- COIHFOIC nyl acetate copolymer having a melt index of 0.8 A semi-conductingcomposition was prepared using dgm/min. and a vinyl acetate content ofabout four per 63.8 parts of the copolymer used to prepare Control Acent by weight, and 20 parts ofthe terpolymer. 36 parts and 36 parts ofthe same carbon black and 0.2 part of of the carbon black and 0.2 partof the stabilizer used the same stabilizer used to prepare thecomposition of in Example I. This composition had the properties ExampleI. This control contained a copolymer having shown in the table.

EXAMPLES CONTROLS l 2 3 A B c D Brittleness. F fC. -50 -45 45 -35 -25-35 -25 Sccant Modulus. psi X It)" 39.4 36.l 47.8 I43 52vl 19.7 45.6

Tensile strength. psi

original [730 l9l0 I880 1340 1750 1390 I640 aged. 7 days at 100C. I850430w) l(16(l(al 1470 2040 1570 1x50 Elongationf/i original 350 400 400290 m0 355 I70 aged. 7 days at l00('. 270 4l0(al 385(a) 280 I 335 I15Oil rcsistanccflr 0.3] l.74(h) l.|3(hl L3 0.4 L0 0.4

Continued EXAMPLES CONTROLS 1 2 3 A B C D Volume resistivity, ohm-cm Iat 23C. 11.9 15.6 87.0 22.7 11 26 14.1 17.2 76.5 89.0 45.9 15 7 74.5 198 43.3 108.5 92.8 229 25.1 343 39 274.0 395.7 130.2 1765 157 1970 1621185 850.3 282.8 3722 1589 5844 737 Stress crack failure 0 20 0 0 0Dcformationffi at 75C. 0 3.2 0 2.11 0 90 0.5 31 5 0 27.2 0 10.5 67 0 3.168.3 0.69 71.2 72.9 32 75.4 2.8

(an) aged 14 days (h) ASTM No. 3 oil used What is claimed is:

l. A semi-conducting composition of:

i. a copolymer of ethylene and ethyl acrylate or vinyl acetate comonomerhaving a comonomer content of 2 to 5 weight per cent,

ii. an ethylene-propylene-termonomer elastomer in an amount of from 3 to20 weight per cent of said composition, and

iii. a conducting carbon black in an amount of from 25 to 50 weight percent of said composition.

2. A semi-conducting composition as claimed in tate.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,849,333 Dated November 7 19, 1974 Inventor-(s) Lloyd et It iscertified that error appears in the above identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the title, line 3, "ethylarcralate" should read ---ethyl acrylate---.

--contain---.

Signed and sealed this 21st day of Jannary 1975.

[SEAL] Attest:

MCCOY M. I GIBSON JR. Attesting Officer C. MARSHALL DANN Commissioner ofPatents USCOMM-DC 6037 B-PGQ FORM PO-105O (10-69) I 9 \LS. GOVERNMENTPRINTING OFFICE I959 0-356-334,

1. A SEMI-CONDUCTING COMPOSITION OF
 1. A COPOLYMER OF ETHYLENE AND ETHYLACRYLATE OR VINYL ACETATE COMONOMER HAVING CONTENT OF 2 TO WEIGHT PERCENT, II. AN ETHYLENE-PROPYLWNE-TERMONOMER ELASTOMER IN AN AMOUNT OFFROM 3 TO 20 WEIGHT PER CENT OF SAID COMPOSITION, AND III. A CONDUCTINGCARBON BLACK IN AN AMOUNT OF FROM 25 TO 50 WEIGHT PERCENT OF SAIDCOMPOSITION.
 2. A semi-conducting composition as claimed in claim 1wherein the comonomer content in the copolymer is from 3 to 5 weight percent.
 3. A semi-conducting composition as claimed in claim 1 wherein thecopolymer has a melt index below 3.5 decigrams per minute.
 4. Asemi-conducting composition as claimed in claim 1 wherein the copolymeris ethylene-ethyl acrylate.
 5. A semi-conducting composition as claimedin claim 1 wherein the copolymer is ethylene-vinyl acetate.